1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head for use in thermally-assisted magnetic recording to write data on a recording medium with the coercivity thereof lowered by irradiating the recording medium with near-field light.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head unit including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider configured to slightly fly above the surface of a recording medium. The slider has a medium facing surface configured to face the recording medium. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end).
Here, the side of the positions closer to the leading end relative to a reference position will be referred to as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be referred to as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, disadvantageously reduces the thermal stability of magnetization of the magnetic fine particles. To resolve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To resolve the foregoing problems, there has been proposed a technology called thermally-assisted magnetic recording. The technology uses a recording medium having high coercivity. When writing data, a write magnetic field and heat are simultaneously applied to the area of the recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The laser light to be used for generating near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near the medium facing surface of the slider.
U.S. Patent Application Publication No. 2011/0170381 A1 discloses a thermally-assisted magnetic recording head including a main pole, a waveguide and a plasmon generator. The main pole has an end face located in the medium facing surface, and produces a write magnetic field from this end face. The plasmon generator has an end face located in the medium facing surface. The waveguide includes a core and a cladding. In this head, the surface of the core and the surface of the plasmon generator face each other with a gap interposed therebetween. This head is configured to excite surface plasmons on the plasmon generator by using evanescent light that occurs on the surface of the core based on the light propagating through the core, and to cause near-field light to be generated from the end face of the plasmon generator based on the excited surface plasmons.
In a thermally-assisted magnetic recording head, the plasmon generator and the main pole become hot due to heat generated by the plasmon generator. This results in the problem of deformation or breakage of the plasmon generator, thus shortening the life of the thermally-assisted magnetic recording head.
One of solutions to the aforementioned problem is to construct the plasmon generator to include a first metal portion and a second metal portion that are formed of different metal materials, as disclosed in U.S. Patent Application Publication No. 2011/0170381 A1. The first metal portion is not exposed in the medium facing surface, whereas the second metal portion is exposed in the medium facing surface. The aforementioned problem can be resolved by, for example, forming the second metal portion of a metal material harder than that of a metal material used to form the first metal portion.
To achieve higher recording density, it is necessary to make the track width smaller by reducing at least one of the width of the end face of the plasmon generator in the medium facing surface and the width of the end face of the main pole in the medium facing surface. As the track width is reduced, it becomes more important to bring the end face of the plasmon generator and the end face of the main pole into precise alignment with each other.
U.S. Patent Application Publication No. 2011/0170381 A1 discloses a technique to form a plasmon generator by etching a metal layer using either the main pole or a mask for use to etch the main pole. This technique allows for precise alignment of the end face of the plasmon generator and the end face of the main pole with each other. When employing this technique, however, any attempts to reduce the track width would result in a reduction in the width of the end face of the main pole, and this would cause the main pole to become unable to pass much magnetic flux and thus unable to produce a write magnetic field of sufficient magnitude from its end face. A further problem with the aforementioned technique is that it is difficult to permit a desired sizing of the width of the end face of the main pole without limitations imposed by the width of the end face of the plasmon generator.